Communication relating to the spread-spectrum code division multiple access, widely studied is the soft handoff technology for preventing the communications from being interrupted by being transmitted and received the same signals simultaneously between two base stations when a mobile terminal moves from one cell to an adjacent cell. As the prior art relating to a coordinated transmission, for example, a system described in the patent document 1, the following non-patent document 1, etc. is disclosed. In the prior art, a coordinated transmission system for successfully increasing the link capacity is disclosed.
Based on a similar concept, a coordinated transmission system using a distributed antenna arranged in a different base station is proposed in relation to the multi-input and multi-output (MIMO) technology corresponding to macroscopic fading. As the prior art obtained by combining the MIMO technology and the coordinated transmission technology, for example, the systems described in the following non-patent documents 2 through 6 are proposed. These systems aim at attaining both a macroscopic diversity effect and a MIMO effect.
The discussions of the macroscopic diversity with a coordinated transmission have been made in a planning project of a new mobile telephone communication standard such the LTE (Long Term Evolution) etc. for which a standardizing operation is performed by a standardizing organization 3GPP (3rd Generation Partnership Project), for example. These discussions are disclosed by, for example, the following non-patent document 7. However, since it has been hard to distribute data of a high layer to different base stations, the coordinated transmission has not been realized, but a system of distributing data only to one base station has been used for simple implementation.
Recently, the LTE advanced standard as a next generation standard of the LTE has been developed as the fourth generation system (4G). In the standard, especially at a system performance request relating to the frequency efficiency for downlink (DL) and uplink (UL), a rather positive target is set. A practical discussion of the problem above has been disclosed in, for example, the following non-patent document 8.
To attain the above-mentioned target, some corporations have presented useful propositions about a beam forming transmission, intra-cell interference control, and relay control. In the propositions, the point of the discussion relating to the coordinated transmission has been taken up again to reconsider the possibility of the implementation. To be concrete, it is disclosed in, for example, the following non-patent document 9 or 10. In the LTE advanced, the target of the throughput of a user at the edge of a cell is set as approximately 1.4 times as high as that in the release 8 of the LTE communication standard. By taking this into account, the coordinated transmission system is expected as an important candidate in the LTE advanced technology.
Before adopting the coordinated transmission technology in the next generation communication standard such as the LTE advanced etc., there are a number of points to be discussed. It is, for example, a search of data and control channel, transmission timing, user packet scheduling, hybrid automatic repeat request (HARQ) process, etc. between eNodes-B through the X2 interface. The most important search among them is that relating to the HARQ.
In the LTE communication standard etc., the packet communication technology is required to enable the high-speed communications at a mobile terminal. In the packet communication, a reception device receives communication information while detecting an error based on the error correction code added to a communication packet by transmission device. Then, the reception device returns to the transmission device an ACK (acknowledgement) or a NAK (negative acknowledgement) about the reception status of the communication packet. The transmission device retransmits transmission information when the reception device returns a NAK or when no transmission status confirmation can be received before a certain period has passed after a packet is transmitted.
In the HARQ technology adopted in the LTE etc., for example, the retransmission pattern is determined on the transmission device side after considering that the data whose decoding has failed by the reception device is not discarded but decoded by a combination with retransmission data in the process of a layer 1 protocol hierarchical level of the LTE etc. On the reception device side, the data whose reception has failed is not discarded, but decoded by a combination with retransmission data. Thus, retransmission control is realized with high efficiency and high accuracy.
Therefore, in the next generation packet communication system, it is an important problem to determine how the HARQ is to be realized in the coordinated transmission system to realize a coordinated transmission system with a high diversity effect.
However, in the prior art disclosed as Patent Document 1 or non-patent documents 1 through 10, no practical technology for realizing the HARQ in the coordinated transmission has not been disclosed.
In addition, the system described in the following patent document 2 is disclosed as prior art obtained by combining the HARQ and the MIMO technology. Patent Document 2 refers to a practical system for realizing the HARQ in the packet transmission using a MIMO multiple transmission antenna.
However, the MIMO is based on that a plurality of antennas are accommodated in one base station while the coordinated transmission is based on that the antennas of a plurality of base stations arranged in a distributed manner perform a coordinated transmission in the downlink direction toward a mobile terminal. To realize a coordinated transmission including a HARQ between the base stations arranged in the distributed manner, it is necessary to solve the problems, which is not necessary in the MIMO, of the communication system for user data and channel data, timing, etc. among the base stations. Especially, the combination of a new data packet and a retransmission data packet in the HARQ with the coordinated transmission is not disclosed by the above-mentioned prior art, which remains as an unsolved problem.
Patent Document 1: National Publication of International Patent Application No. 2008-503974
Patent Document 2: National Publication of International Patent Application No. 2008-517484
Non-patent Document 1: A. J. Viterbi, A. M. Viterbi, K. S. Gilhousen, and E. Zehavi, “Soft handoff extends CDMA cell coverage and increases reverse link capacity”, IEEE J. Sel. Areas Commun., vol. 12, pp. 1281-1288, October, 1994.
Non-patent Document 2: W. Roh and A. Paulraj, “MIMO channel capacity for the distributed antenna systems”, in IEEE VTC′ 02, vol. 3, pp. 1520-1524, September 2002.
Non-patent Document 3: Z. Ni and D. Li, “Impact of fading correlation and power allocation on capacity of distributed MIMO”, IEEE Emerging technologies: Frontiers of Mobile and Wireless Communication, 2004, Volume 2, May 31-Jun. 2, 2004 Page(s): 697-700 vol. 2.
Non-patent Document 4: Syed A. Jafar, and S. Shamai, “Degrees of freedom region for the MIMO X Channel”, IEEE Transactions on Information Theory, Vol. 54, No. 1, pp. 151-170, January 2008.
Non-patent Document 5: D. Wang, X. You, J. Wang, Y. Wang, and X. Hou, “Spectral Efficiency of Distributed MIMO Cellular Systems in a composite Fading Channel”, IEEE International conference on, Communications, 2008. ICC '08, pp. 1259-1264, May 19-23, 2008.
Non-patent Document 6: O. Simeone, O. Somekh, H. V. Poor, and S. Shamai, “Distributed MIMO in multi-cell wireless systems via finite-capacity links”, Communications, Control and Signal Processing, 2008. ISCCSP 2008. 3rd International Symposium on, pp. 203-206, Mar. 12-14, 2008.
Non-patent Document 7: 3GPP TR 25.814 v7.0.0. Physical layer aspects for evolved UTRA, release-7, June 2006.
Non-patent Document 8: 3GPP TR 36.913 V7.0.0, Requirements for Further Advancements for E-UTRA, release-8, V8.0.0, June 2008.
Non-patent Document 9: 3GPP TSG RAN WG1 Meeting #53bis Warsaw, Poland, “Collaborative MIMO for LTE-A downlink”, June 30-Jul. 4, 2008, R1-082501.
Non-patent Document 10: 3GPP TSG RAN WG1 Meeting #53bis Warsaw, Poland, “Network MIMO Precoding”, June 30-Jul. 4, 2008, R1-082497